1. Field of the Invention
The present invention relates to a color conversion definition coupling apparatus for creating a coupling color conversion definition defining an association of coordinates of a first device color space depending on a first device with coordinates of a second device color space depending on a second device in such a manner that coordinates of a device color space depending on a device mediating between an image and image data is associated with coordinates of a non-dependence color space independent of a device, and a first color conversion definition and a second color conversion definition, which define the first device and the second device, respectively, are coupled with one another, and a color conversion definition coupling program storage medium storing a color conversion definition coupling program which causes a computer to operate as a color conversion definition coupling apparatus, when the color conversion definition coupling program is incorporated into the computer and is executed.
2. Description of the Related Art
There are known various types of input devices for deriving image data upon receipt of an image, for example, a color scanner for deriving image data upon reading of a recorded image, and a digital still camera (DSC) for deriving image data by means of reading through formation of an image of the subject on a solid state imaging device. According to those input devices, image data is represented by data of a range of for example 0 to 255 on each of three colors for example of R (red), G (green) and B (blue). This range represents a range of colors, which can be dealt with as hardware in the input device. However, there is a limit to colors, which can be represented by numerical values within determined ranges on three colors of R (red), G (green) and B (blue). For this reason, even if a color of the original image involves extremely plentiful expression, once conversion into image data by the input device may restrict the image represented by the image data to colors within the color expression area represented by a cube and a rectangular parallelepiped within R, G, B color spaces, which can be dealt with in the input device.
With respect to an output device for outputting an image in accordance with image data, there are known various types of output devices, for example, a photographic printer for recording an image on a photographic paper in such a manner that the photographic paper is exposed with a laser light and the exposed photographic paper is developed, a printer for recording an image on a paper in accordance with an electrophotographic system and an ink jet system, a printing machine for creating a large amount of printed matters through running a rotary press, and an image display unit for displaying an image on a display screen in accordance with image data, for example, a CRT display and a plasma display. Also with respect to those output devices, in a similar fashion to that of the above-mentioned input device, there are color representation areas according to the respective output devices. That is, the output devices can represent various colors in accordance with image data representative of three colors for example, R, G and B, and image data representative of four colors of C (cyan), M (magenta), Y (yellow), and K (black). However, the range of colors, which can be dealt with as hardware in the output device, is restricted to colors within the color representation area (for example, a color representation area represented by numeral values of 0 to 255 on each of three colors of R, G and B) represented by a cube and a rectangular parallelepiped of output device color spaces (for example, RGB color spaces, and CMYK color spaces). The color representation areas in the input device and the output device are referred to as a color gamut.
By the way, recently, it is increased that image data is used on a common basis among various sorts of input devices and various sorts of output devices, and there is known a method in which when the input devices and the output devices are connected with one another to apply the image data, colors of image data are kept equal. There is known, for example, a method in which the association between coordinates of a device color space depending on a device and coordinates of a device independent color space (a space of device independent data: for example, L*a*b* color space) independent of a device is defined by an association table referred to as a profile and is prepared for each of sorts of the input devices and the output devices, and a combination profile coupling profiles for devices, in which image data is applied, to one another is used to perform a conversion of image data.
However, an application of image data in the manner of maintaining colors of the image data of equality may bring about an omission of color representation at the portion in which the color representation area is of discordance, since the color representation area is varied for each of the devices as mentioned above. A large omission of the color representation may bring about unnaturalness of the image represented by the applied image data.
On the other hand, it is empirically known that regardless of discordance of the color representation area, various types of devices can represent the essentially same image in form of visually natural images. The natural images represented by the various types of devices are represented with colors, which are somewhat different from one another in accordance with a difference between the color representation areas of the devices. However, images represented by any of the devices may give the natural impression, because adaptability of person's eyes is high.
Thus, when image data is applied, there is needed a color conversion to convert colors of images to maintain the natural impression for the images. It is desired for such a color conversion that the respective colors in the color representation areas (color gamut) of a certain device are completely associated with the respective colors in the color representation areas (color gamut) of another device. Such a color conversion is referred to as a gamut mapping.
Hitherto, as the color conversion (gamut mapping), there are proposed various methods of performing the gamut mapping on the independent color space (for example, Japanese Patent Application Laid Open Gazette TokuKai Sho. 60-105376, Japanese Patent Application Laid Open Gazette TokuKai Sho. 61-288662, and Japanese Patent Application Laid Open Gazette TokuKai Hei. 4-196675)
Further, according to ICC (International Color Consortium), there is proposed a format in which a conversion definition section defining on a non-dependence color space coordinate conversion between a color reproduction area depending on a device and a coupling area (Profile Connection Space: PCS) independent of a device is incorporating into the above-mentioned profile. Conversion of image data using the coupled profile coupling this format of profiles with one another makes it possible to implement the gamut mapping.
However, according to the technology proposed by the ICC, since no strict definition for the coupling area exists, there is a high possibility that a plurality of sorts of profiles supposing different coupling areas exists. In the event that mutually different sorts of profiles are coupled with one another in accordance with the conventional scheme, the difference between the coupling areas would cause inconvenience in the gamut mapping.